【作者】 焦晋峰；

【导师】 雷宏刚；

【作者基本信息】 太原理工大学 ， 结构工程， 2013， 博士

【摘要】 鉴于平板网架结构的众多优势,在我国不论其应用的规模还是数量上,均稳居世界前列。在平板网架结构上设置悬挂吊车,悬挂吊车所产生的反复交变荷载给网架结构带来疲劳问题。平板网架结构的疲劳主要包括杆件、焊接空心球及悬挂吊点连接的疲劳,而悬挂吊点连接的疲劳是平板网架结构疲劳破坏的关键部位。十字形板一焊接空心球连接作为悬挂吊点的主要方式之一,相关的疲劳理论研究及疲劳试验研究进展较为缓慢,且相关悬挂吊点的疲劳设计计算方法在我国现行的规范和规程中属于空白。上述种种因素给悬挂吊车在平板网架结构中的推广应用造成了很大的制约。在两项国家自然科学基金项目(50678109,51178286)的大力资助下,本文重点针对焊接空心球节点平板网架结构中十字形板—焊接空心球悬挂吊点的疲劳性能进行理论与试验研究。其相关的工作及结论总结如下：1、采用ANSYS有限元软件,以不同规格匹配而成的25个十字形板—焊接空心球节点(材质均为Q235B)为研究对象进行单因素分析,重点讨论了节点相关尺寸的五个因素,即焊接空心球直径D、焊接空心球壁厚tx、十字形板宽度B、十字形板厚度tp和板球连接焊缝焊脚尺寸hf对节点应力的影响。基于分析结果,建立了十字形板—焊接空心球节点的热点应力集中系数的计算公式,其取值区间为3.176～5.365。研究结论揭示了应力集中和疲劳破坏源的关系,解释了十字形板—焊接空心球节点疲劳强度相对较低的原因,为建立以热点应力幅为参量的疲劳设计方法奠定了一定的理论基础。2、设计了与本次疲劳试件相匹配的加荷装置,采用Amsler疲劳试验机(瑞士),顺利完成了25个十字形板—焊接空心球节点的常幅疲劳性能试验,得到了25个疲劳试验数据(6个异常)。收集了国内已有的9个常幅疲劳试验数据。将本文与国内共有的28个疲劳试验数据回归统计分析,得到了s-N曲线。3、基于得到的常幅S-N曲线,以热点应力和热点应力幅为设计参量,建立了平板网架结构十字形板—焊接空心球节点两种表达形式的常幅疲劳设计方法；若以N=2×106为基准期,则[△σ]2×106=19.66Mpa,[△σh]2×106=62.44Mpa；上述常幅疲劳设计方法的建立为国家相关规范或规程提供了有益的补充,扩大了节点疲劳设计方法的的类别。4、为了揭示十字形板—焊接空心球节点的变幅疲劳性能,采用代表性的加载模式对14个节点疲劳试件进行变幅试验,试验共取得14个有效的疲劳试验数据。通过对上述试验数据进行处理,采用线性累积损伤理论Miner法则和(?)Corten-Dolan非线性累积损伤理论分别对其变幅疲劳试件进行寿命估算,结果表明：采用Corten-Dolan理论对十字形板—焊接空心球节点进行疲劳寿命估算较为合理。5、借助于电子显微镜和放大镜,进行了4个常幅和4个变幅典型疲劳试件疲劳断口的金相分析；揭示了十字形板—焊接空心球节点常幅和变幅疲劳破坏机理及断口特征,常幅疲劳断口的随机性远小于变幅疲劳断口；结合理论分析和金相分析,得出十字形板—焊接空心球节点中板肋端部是疲劳源的主要起始部位。6、采用断裂力学对十字形板—焊接空心球节点进行疲劳寿命估算是可行的。理论估算值与试验结果的规律基本一致,但理论估算值与试验结果两者数值存在一定的误差,最大相差为30%；节点所含的先天性缺陷或类裂纹的大小对裂纹扩展寿命影响很大,但材料的断裂韧性对疲劳寿命影响较小。更多还原

【Abstract】 In view of the many advantages of plate-type grid structure, application in our country, regardless of the scale or quantity, ranks front of the world. Suspending crane is set up in plate-type grid structure. Alternating load produced by suspending crane brings fatigue problem to the plate-type grid structure. Plate-type grid structure fatigue mainly includes the fatigue of bar, welded hollow sphere and hanging point connection. And the fatigue of the hanging point connection is the key part of plate-type grid structure fatigue damage. Crossed plate-welded hollow spherical connection as one of the main hanging point form, its theoretical and experimental study is less, and relevant fatigue design method is not established in the current national rules and regulations. As a result,it seriously restricts the extensive use of suspending crane in industrial buildings.In this thesis, based on the National Scientific and Natural funds (50678109,51178286), the fatigue performance of crossed plate-welded hollow spherical node in plate-type grid structure was analysed in theory and experiment. The related work and conclusion are as follows: (1) By means of the software ANSYS,25different crossed plate-welded hollow spherical nodes (sourced for Q235B) were analysed with20nodes of SOLID95entity model. And the influence of welded hollow ball diameter-D, welded hollow ball thickness-ts、cross-shaped board width-B, crossed plate thickness-tp and weld leg size-hf are discussed detailedly. Calculation formular of the stress concentration factor of crossed plate-welded hollow spherical node is established and the value ranges in3.176～5.365. Research result reveals the relationship between stress concentration and fatigue damage source, explains that why the crossed plate-welded hollow spherical node fatigue strength is extremely low, and sets up a theoretical foundation for fatigue design method on the basis of hot stress amplitude.(2) Designing the loading device that matchs the fatigue specimens, using Amsler fatigue testing machine (Switzerland),we successfully completed the constant amplitude fatigue test of25crossed plate-welded hollow spherical node s, and the fatigue test data were obtained(six data were abnormal). By Collecting the pre-existing domestic nine constant amplitude fatigue test data, the thesis got the S-N curve with regression statistical analysis of a total of28fatigue test data.(3) Based on the S-N curve, with hot spot stress and hot spot stress amplitude as design parameters, two kinds of constant amplitude fatigue design method of crossed plate-welded hollow spherical node in plate-type grid structure are established. If N=2×106, it gets [△σ]2×106=19.66MPa and [△σh] 2×106=62.44MPa.The establishment of constant amplitude fatigue design method provides beneficial supplement for relevant national codes or specifications, and expands the categorys of node fatigue design method.(4) In order to reveal the variable amplitude fatigue performance of crossed plate-welded hollow spherical node,14node fatigue specimens were tested for variable amplitude by typical load pattern, and14effective fatigue test data were obtained. Through dealing with the test data, using the laws of Miner linear cumulative damage theory and Corten-Dolan nonlinear cumulative damage theory, the life estimation of variable amplitude fatigue specimens were respectively gotten.The result shows that the adopting of Corten-Dolan theory to cross plate-welded hollow spherical node for fatigue life estimation is reasonable.(5) By means of magnifier and electron microscopy, metallographic analysis of the4typical constant amplitude and4variable amplitude fracture section were done.It reveals the fatigue failure mechanism of crossed plate-welded hollow spherical node under constant amplitude and variable amplitude and fracture characteristics,and the randomness of constant fatigue fracture is often far less than the variable amplitude fatigue fracture; Combined with the theoretical and metallographic analysis,it gets the result that the end of crossed plate is the main fatigue damage origin.(6)The calculation for the fatigue life of crossed plate-welded hollow spherical connection by using fracture mechanics is feasible. Theoretical estimate and experimental result are basically identical, it has a certain error between them.The error is in30%or so. The initial crack length of node has a large influence on the crack development life, and the fracture toughness has a small influence on fatigue life.更多还原